Water treatment: a case-by-case approach

Chemicals are omnipresent, in municipal treatment works, in wastewater and drinking water networks, and in industrial units where they adapt the composition of the water to suit a particular use. Their use is not a recent phenomenon. With the appropriate formulation they can make the treatment more effective. Today, chemicals can be adapted to suit highly specialised applications. Their formulations continue to evolve. In this flourishing market, they offer improved performance coupled with reduced environment impact. Optimising the pairing of chemical/equipment is definitely the profession's latest priority. “At Degrémont, 50 chemists and microbiologists work with nearly 300 research workers at Suez Lyonnaise des Eaux water research centres on developing new formulations and optimising the synergy between treatment product and equipment”, explains Pascal Remy, President of Aquazur. At Aquarex, this approach is also a priority.

Firms in the water treatment sector no longer confine their activities to simply marketing a product, and increasingly seek to provide a solution to a given problem.

Georges Marron, Managing Director of Aquarex, a subsidiary of OTV: "This work is extremely important."

The choice of product is closely linked to the quality of the water. The slightest variation in one of its parameters, such as the pH or temperature, leads to a change in the chemical reactions involved, and therefore affects the treatment.

Moreover, the amount of sludge produced will depend on the formula that is chosen and the process used.

The quality of the sludge will determine whether it can eventually be used for spreading, which accounts for the care that must be taken in deciding what type of additional chemical treatment to use.

For the treatment of drinking water, additional rules apply. Clearly, the chemical used in the preparation of drinking water must not contain products that are harmful to human health.

Product formulation and maximum dose are strictly supervised. European standards are currently being drafted for some reagents. "They should formalise the role of the reagent, define the chemical composition of the product, analytical methods and labelling", states Michel Faivre of Anjou Recherche.

Although the market tends to be covered by an increasing number of standards, there is still a considerable potential for even more effective formulae having no adverse effects on the environment.

With this in mind, firms are endeavouring to develop reagents that are more effective, have fewer side effects, are more economical and are easy to use. Formulations are constantly improving and are specifically adapted to the process. It is becoming increasingly common for the many researchers working on these formulae to customise them for a specific application. They provide the solution to a problem and are marketed with implementation included.

"The most crucial thing in water treatment applications is to use the right dose of the chosen reagent", as Philippe Denis of Anjou Recherche points out, even for the most common applications such as clarification.

Water clarification

In water clarification, the association of coagulant/flocculant comes into play. It is used to reduce turbidity through precipitation (or flotation) of organic material.

The traditional treatment consists of dosing with iron or aluminium salts to coagulate the organic material. Polymers are also used and produce better results in cold water. Adding these products helps to prepare the water for effective disinfection by reducing as far as possible the amount of material in suspension that can provide support for microorganisms.

Up to now, iron chloride has been widely used to purify and clarify urban and industrial wastewater. It acts immediately by flocculation of particles in suspension in the water; in other words, it causes them to coagulate and settle in the form of coarse floccules. This operation traps phosphates involved in eutrophication of water, while at the same time improving the performance of biological treatment. Its thickening action facilitates the treatment of waste sludge, especially when used with lime. However, the situation could well change when the new regulations on sludge come into force. "Nowadays, the complaint is that it produces two or three times as much sludge as the latest formulations", explains Georges Marron.

At this level, the choice of chemical affects the entire treatment cycle, and more particularly the sludge treatment phase. “The dewatering of sludge is becoming more and more of a problem. The techniques used are changing and this means that the products will have to evolve. To optimise centrifugation, more highly specialised polymers are needed”, notes Jean-Louis Paulus-Lemoine, Head of Marketing at Aquazur. “At the same time, regulations on spreading are becoming more stringent on toxicity levels. The mineral salt content of traditionally used products could therefore prove a problem because of their levels of iron or aluminium.”

Organic flocculants/coagulants should be able to meet the new requirements. They generate less sludge than mineral salts and might eventually replace iron or aluminium salts. Buckman Laboratories is working along these lines. Frédéric Delord, French water treatment specialist at Buckman Laboratories explains: “We have developed a new generation of more efficient coagulants. By associating mineral salts with bound organic polymers, these coagulants produce less sludge, in the region of a 20 to 40 % reduction in volume”.

However, this is not the only role of chemicals. They are essential for the equilibrium of the water and make it less aggressive and less scale-forming.

Balancing drinking water

In granite areas the water is too acidic, whereas in limestone areas it is too alkaline. In the natural state it may also contain undesirable atoms. Should this natural resource stray from the accepted chemical standards, it can lead to a number of chemical reactions. This may result in by-products that are more or less toxic for humans and in network dysfunction due to corrosion or scaling. To control these phenomena, the water has to be balanced by bringing it as close as possible to a pH of 8 and/or by remineralisation. However, great care is needed. The operation is designed to limit chemical reactions and has to be performed on a case-by-case basis. Since it influences the conditions under which disinfection takes place, it is essential to obtain the right balance.

A pH imbalance in the water can be corrected through the addition of acids or alkalis, for example using hydrochloric acid or sodium hydroxide. To complete the treatment, sodium bicarbonate is used for remineralisation or sodium chloride for softening.

“To optimise the chemical treatment, it is essential to have a perfect knowledge of the characteristics of the raw waters before any balancing is undertaken”, explains Philippe Denis, of Anjou Recherche.

The choice of chemicals will be based on these data. For regions where the water is highly mineralised, steps need to be taken to keep scaling to a minimum.

In France, a scale preventive whose formula has been approved by the Ministry of Health is used.

For the production of drinking water, Aquarex has developed formulations for cationic anticlogging products, which are awaiting approval.

In regions where the water is only lightly mineralised, the problem is quite different. The pH has to be increased to reduce the corrosive action of the water, especially in regard to the steel, lead and cast iron found in the network and connections. Without treatment this will result in ferruginous water, with a high iron and lead content. There is a deterioration in water quality and it corrodes the pipes.

There are several ways of reducing this effect: raising the pH, remineralisation and film forming processes with a corrosion inhibitor.

Orthophosphates belong to the last named category. At low doses, between 1 and 5 ppt, they provide an effective treatment at a cost (0.06 to 0.08 FRF per m³ of water treated) that is very much lower than the cost of replacing the network.

These chemicals, which are already used in exceptional circumstances, might eventually provide a solution to the problem of lead.

Solving the lead problem

In France, the arrival of the new EC Directive on water poses a tricky problem over lead. By adopting the WHO reference value of 10 µg/l as the maximum permitted level of lead in drinking water at the tap, to be achieved within 15 years, the new regulation is already raising many problems.

Over and above the question of sampling and analysis (see boxes), the cost of complying with this ceiling could be anywhere between 10 and 50 billion French francs. It will involve changing a great number of connections (particularly in old, dilapidated buildings) unless a rapidly applicable treatment can be found to reduce the amount of lead being dissolved. The entire water treatment sector is currently working on possible solutions.

Orthophosphates could prove to be a medium-term solution to the problem. According to Pierre Schulhof, Managing Director of Anjou Recherche: “Orthophosphates provide a reasonable compromise. Even if we are unable to reduce levels to zero, they probably represent the most likely prospect. They will allow the transitional level of 25 µg/l to be met while awaiting the replacement of connections”.

At Degrémont, the formulations are developed with Cirsee, the research centre at Lyonnaise des Eaux. “Phosphates can resolve the lead problem, and we are able to respect 25 µg/l”, states Pascal Remy.

Sagep (Société Anonyme de Gestion des Eaux de Paris) is also working on the problem. “We are conducting feasibility trials to find a solution”, explains Antoine Montiel, Doctor of Science, in charge of the Scientific Mission on Water Quality at Sagep. “Trials began in mid-March 1998. The first results should be available in autumn”.

Even though treating water with orthophosphates may solve the problem, it is likely to raise other unknowns in terms of disinfection. The higher the pH, the greater the quantity of chlorine that has to be added, or else a different disinfectant must be used.

…use chlorine dioxide, but this poses other problems. A compromise will therefore have to be found,” explains Pierre Schulhof. Furthermore, the wider use of phosphates, which act as a nutrient, can have other consequences, such as the regrowth of microorganisms. This point is the subject of research currently being conducted by Professor Block at the University of Nancy (France), on behalf of Anjou Recherche. The aim is to determine whether orthophosphates encourage the development of biological flora and bacteria in the network. “If the results are favorable, we shall apply to the relevant authorities to have the products licensed”, states Pierre Schulhof.

All these studies are being conducted at a rapid pace since the stakes are particularly high. Yet, as Pascal Remy points out: “the water treatment market is mainly concerned with the treatment of industrial waters”. The industrial sector is a highly coveted market.

Industry, a highly coveted market

To meet their requirements, many factories draw raw water from natural sources. The water then has to be treated to adapt it to suit the process. For this purpose, chemicals occupy a key position. Coagulants/flocculants and products to balance the water are very widely used.

At the other end of the production line, effluents have to be treated before being discharged into the sewers or the environment. Here, too, chemicals are often used, to deal with the kind of problems that are specific to each industry. Heavy metals are a case in point. To precipitate heavy metals in solution and concentrate them in sludge, Degussa offers a formula called TMT 15. This is a trimercapto-s-triazine sodium salt in aqueous solution which, when mixed with the effluent, precipitates all the heavy metals.

Between these two extremes, there are many processes that need specially adapted water. This is the case with boilers, cooling systems, heat exchangers, etc., which require water that has been specially treated to reduce scaling and corrosion. This is also true of certain processes, in the agri-food sector for instance, where the water must be free from microorganisms.

Disinfection

Chlorine and sodium hypochlorite are very widely used for disinfecting water. They prevent the proliferation of microorganisms, algae and some types of small mollusks. Due to their persistence, these two bactericidal products ensure the continued microbiological quality of the water.

Peracetic acid is beginning to establish itself on the French market. It is not persistent. It reacts on itself by a self-sustaining reaction.

The choice of formulation must be made to suit the equipment and the calculations made under peak conditions.

The molecule simply breaks down into water, oxygen and carbon dioxide. It is therefore harmless for the environment. At Solvay they point out that “it destroys all microorganisms except for Coccidia”. It is therefore recommended wherever its use is appropriate.

The future regulations on drinking water are expected to impose a limit on lead content of 10 µg per liter to be achieved within 15 years. It is not currently possible to meet this excessively low ceiling without eliminating the lead piping and tin/lead welding still present in the network (public or private). An alternative solution is being explored in France by the IRAP materials department at CTTM (technology transfer centre at Le Mans). It entails the development of a procedure for lining lead pipes. The aim is simple. By covering the inner surface of the pipe with a polymer film, the lead is no longer in contact with the water. The problem is thus eliminated.

To achieve this aim, the CTTM first has to resolve a number of problems. The polymer must:

• be waterborne,
• be of food-grade quality,
• adhere well to lead,
• not have any particular organoleptic qualities.

After having reviewed all the polymers in aqueous phase, a food-grade quality hydrophobic industrial latex was selected.

“Once the material had been chosen, it remained only to validate the concept and develop a simple method of application that can be used by plumbers”, explains Guy Boccacio, research and development engineer in charge of the project.

Powerful action and lack of persistence are desirable, as in the treatment of effluents discharged into the natural environment, process waters in closed systems and installations in the agri-food industry.

However, although there are currently a large number of biocides, the European Community may eventually decide to restrict the number. “The aim is to reduce the number of chemicals and the formulations based on them”, explains Pascal Remy, saying that “in replacement, we are currently witnessing the development of enzymatic biocides, but they are less efficient and more expensive”.

This view is not shared by Frédéric Delord: “At Buckman Laboratories we think that enzymes will eventually replace biocides, because they are an ecological and non-toxic solution to the problem of contamination by microorganisms”. The firm is already marketing enzyme-based solutions that it considers to be “less expensive and technically more effective”. When it comes to enzymes, Buckman Laboratories are already experienced. In 1996, in a quite different field, the firm received an award from the French Paper Production Industry Technical Association, within the framework of international meetings of the paper industry, for the treatment of deposits on paper mills using enzyme-based solutions. This approach made it possible to reduce the use of toxic products to eliminate fouling in the wet part of the process.

For boilers and heat exchangers the problem is slightly different. Here, the water has to be treated to avoid corrosion or scaling within the circuits.

Reducing scaling and corrosion

Cooling systems, heat exchangers and boilers are sensitive to water quality. Mineralised water leads to scaling. In time, a pipe will become blocked and the factory equipment will malfunction. Yet if the mineral content is low, the situation is no better. The corrosive action will risk perforating the circuit. This phenomenon is difficult to detect.

Technology: lining of lead pipes

A procedure for lining lead piping is currently being developed at Le Mans (France). It involves lining the inner surface of the pipe with an inert material.

Elastomer operations at CTTM’s materials department. First, a solution had to be found to the problem of lead carbonate, the scaling which lines all old piping. “This deposit is brittle and is not a suitable substrate for the latex”, notes Guy Boccaccio. A descaling procedure was therefore developed using acetic acid and potash. “We carry out double cleaning, to avoid saturation, alternating with intermediate flushing.” Once the pipe has been descaled, the latex can be deposited. “This is done by filling the conduit with latex, and then emptying it.” A thin layer is left adhering to the wall of the pipe. All that remains is to allow it to dry by maintaining a current of air at room temperature. The procedure is simple, “and throughout the development we have constantly kept in mind the practical constraints of implementation. All the refurbishing work can be completed in less than 24 hours.”

The first series of evaluation trials was conducted at the laboratories of Anjou Recherche (partner on this project) to measure the graining out of lead and to test water flavour. The results were positive. The study is currently entering a more delicate phase. Namely, to transfer the process to a miniature network, presenting all the characteristics of a real installation, with bends, joints, etc. The first results should be available in autumn 1998 and are eagerly awaited.

MOM

especially in view of the considerable development of microbiological corrosion in recent years.

“The classic treatment still in use only a few years ago was first to reduce the pH to around 6 to avoid deposits of CaCO3 and then add a chromate-based biocide,” explains J-E Lamot, Technical Manager for Europe at Buckman Laboratories. “The absence of inorganic deposits and the presence of chromates notably prevented any proliferation of sulphate-reducing bacteria.” The treatment today consists of allowing the pH to reach its natural equilibrium. This is between 8.0 and 9.0. Deposits are then controlled by organic scaling inhibitors, which usually leave a very thin film of calcium carbonate or phosphate on the wall of the pipe.

This substrate is then far more conducive to the development of bacteria than the bare metal. Moreover, a high pH reduces the efficacy of some biocides.

To limit these problems, the water has to be treated. Boiler specialists have long been aware of this problem. They treat the water to avoid scaling and corrosion by reprocessing it.

A case-by-case approach is used and calculations are based on the operating parameters of the industrial equipment (pressure, temperature, pH). “Decarbonatation and total demineralisation followed by thermal deaeration and chemical treatment are the main techniques used,” explains Laurent Saintot, After-Sales Service Manager at Babcock Wanson. This industrial boiler maker proposes water treatment and monitoring for its boilers and heat exchangers when they are installed and for the maintenance contracts.

“The choice of product formulation depends on the equipment and the results of calculations based on peak operating conditions,” adds Laurent Saintot. “Some manufacturing processes also require the use of food-grade quality products, such as in the agrifood sector and certain industrial laundries.” For treatment of this type, the firm markets a complete range of molecules which it uses on a case-by-case basis, such as oxygen scavengers (hydrazine hydrate and sulphites), alkalising agents to disperse carbonated water (caustic soda, polymers), phosphatising agents, dispersing agents (phosphates and polymers), treatment of condensates (neutralising amines, polyphosphates), algicides, fungicides, bactericides, etc.

Degrémont, which is present on the boiler water treatment market through its specialist subsidiaries, markets Solerpon. This range includes: oxygen scavengers, phosphates to prevent scaling, dispersants to maintain material in suspension, iron and aluminium in solid form, alkalising agents and anti-priming, to avoid water or salt spots being drawn into the steam. Cooling systems are also addressed. The firm has thus developed Kemazur. “This is a less polluting formula based on a terpolymer molecule of organic order, which makes the product as effective as phosphate-based products,” explains Jean-Louis Paulus-Lemoine.

As usual, the treatment selected is on a case-by-case basis after careful analysis of the process, operating conditions and chemical characteristics of the water. Which explains why all the manufacturers are considerably expanding their service activities.

Developing service activities

George Marron explains: “At Aquarex, our approach is to carry out an analysis of the entire water cycle so as to identify critical points.” From this a diagnosis can be made. Solutions are provided based on the use of chemical products (though not exclusively) and a monitoring system for critical thresholds is installed.

This approach allows Aquarex to grasp all the problems linked to water management within a firm. For instance: “Paper manufacturers used to find isolated problems occurring two or three times a year, in spring and autumn, and sometimes”

The choice of chemical product is closely linked to the chemical quality of the water. The slightest variation in one of its components leads to a change in the chemical reactions taking place.

During summer storms. The results of a global analysis of the water cycle demons- trated that the occasional sharp loss of consistency in the sludge originated from a malfunction upstream. In fact, during these periods, the raw water contained a high level of material in suspension and

“We act rather like doctors”, states Gilbert Brelet of Permo, “not only do we perform the diagnosis and analytical review, but we provide studies and coun- selling, we carry out an economic review and techni- cal monitoring, and ensure implementation of our products.”

Permo, which has been specialising in water treat- ment for over 75 years, currently has a turnover of 200 MFRF, of which environmental control repre- sents a substantial share.

The firm has always been involved in the application of simple or compound chemical products vital for the protection of industrial installations. “Our expe- rience is in the field of steam, cooling, industrial process and hot water systems, etc. We treat the water directly at point of use.”

With its long experience, Permo does not confine itself to marketing chemical products. The firm's engineers adopt a much wider approach and study the problem of treatment globally. “This point is essential”, explains Gilbert Brelet, “nowadays we need to obtain technical, economic and environmen- tal results. The last point has in fact become funda- mental."

Based on its very extensive experience in the pro- tection of installations, the firm strongly advocates adopting a global approach to the problem.

“We are perfectly equipped with all the necessary tools —technical knowhow, a certified laboratory, additional treatment techniques— and can guaran- tee the result within the framework of a global contract.

organic material, and the operators, faced with the heavy demand for steam in this industry, simply bypassed the filters to avoid them becoming blocked. The raw or filtered water would then poison the ion exchange resins, leading to a sudden increase in the volume of regeneration solutions pumped to the wastewater treat- ment plant. These liquids had a heavy concentration of salts, which directly influenced the viscosity of the polymers used in dewatering and reduced their effec- tiveness, resulting in a loss of sludge consistency.

The solution lay in periodically monito- ring the input/output pressure of filters upstream rather than in a problem with

the polymers used in the wastewater treat- ment plant”. To promote this type of approach Aquarex has developed a special department. “The aim is to move towards supervised management”, added Georges Marron, “The factory produces, and we treat the water. With a single objective: optimising the existing process by choo- sing the right chemical, while ensuring the

functions of storage/logistics, by managing

the treatment plant and providing a solu- tion to problems arising from the recycling of water”.

“To find the right solution you must first make the right diagnosis”, explains Pascal Remy, “and the installation must be moni- tored to ensure results”. At Degrémont, this is an everyday saying. The firm provides the client with full-time resident supervisors. Their job is to keep the material in good working order and optimise water treat- ment. “In this field, the cost of treatment bears no resemblance to the cost of a break- down”. At CERN (European Organization for Nuclear Research), for example, the firm has seconded two full-time technicians. They are responsible for the supervision and control of analyses and the treatment pro- cess for cooling waters and water deminera- lisation on the site.

The firm is now going one step further: “In the mechanical engineering sector we either sell treatment by the cubic metre or undertake to meet specified targets. If we succeed, the firm receives a bonus, but if we fail we are obliged to pay a non-perfor- mance penalty”.

This skid mounted compact boiler plant, for the Venezuelan firm Soredab, incorporates a chemical dosage unit and a water softener.

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